The present invention relates to molded articles based on pyrogenically produced mixed-oxide systems of silicon dioxide and aluminum oxide, the method for their manufacture and their use as catalyst-carriers or as catalysts.
Pyrogenically produced oxides are characterized by their extreme fine-particulate nature and their correspondingly high specific surfaces, their very high purities, spherical particle shapes and the lack of pores. On account of these properties, pyrogenically produced oxides are becoming increasingly significant as catalyst-carriers (D. Koth, H. Ferch, Chem. Ing. Techn. 52, 628 [1980]).
Pyrogenically produced oxides being especially fineparticulate in size, some difficulties are met with when these products are pelletized into catalyst-carriers or catalysts.
The German OLS No. 31 32 674 discloses a procedure for making molded articles using a silica sol as the binder.
Pressing pyrogenically titanium dioxide is known from the German OLS No. 32 17 751 using organic acids or acidically reacting salts as intermediary binders.
It is known from the German patent No. 21 00 778 to use granulates based on pyrogenically produced silicon dioxides as catalyst carriers in the preparation of products such as vinyl acetates.
These known procedures incur the drawback that the molded articles lack the desired optimal properties of crushing strength, pore volume and pore distribution for use in certain specific catalytic reactions, such as vinyl acetate manufacture from ethylene, acetic acid and oxygen or the hydration of ethylene into ethanol.